126 research outputs found
Flow properties of polymeric powders for SLS
No full textIn order to properly take into account real process conditions relevant to Selective Laser Sintering (SLS), the effect
of temperature on the flow properties of polymeric powders was assessed. Shear tests were carried out at
temperatures from ambient values to values close to the melting temperature of the polymeric powders.
Experiments were performed on two powders with similar chemical compositions but with different melting
temperature, very distinct particle shapes and different particle size distributions resulting from different production
processes. Experiments indicate that flowability significantly worsens when temperature rises and approaches a
value of about 20-30°C lower than the melting point of the polymers. These results are in good agreement with
the working temperatures preconized by the SLS machine users. The average intensity of the interparticle forces
is calculated from the powder flow properties and the Bond number is considered to verify the suitability of the
powder in the SLS process
Structure-Photoluminescence Quenching Relationships of Iridium(III)-Tris(phenylpyridine) Complexes
No full textThe synthesis, structural, photophysical, theoretical, and electrochemical characterization of four tris(2-phenylpyridine)-based Ir III complexes are reported. The complexes were functionalized on the pyridine or on the phenyl rings with amide moieties substituted with a tris(ethyl)amine or ethyl groups, thereby yielding a family of compounds with hemicaged or open (without a capping unit but with similar functional groups on the ligand) structure. Within the context of the parent tris(2-phenylpyridine) and the full-cage iridium(III) complexes, structure-photoluminescence quenching relationships (SPQR) of the four complexes have been investigated. Luminescence quenching by oxygen has been studied with Stern-Volmer plots and through evaluation of the thermodynamic parameters involved in the quenching process. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have been performed on the complexes to gain insights into structural and electronicfeatures and the nature of the excited states involved in the electronic absorption processes. Interestingly, shielding by the capping unit of moieties in which the LUMO orbital is mostly localized (on the pyridines) results in a dramatic 40 % decrease in oxygen quenching. Conversely, shielding ofmoieties in which the HOMO orbital is partially localized (on the phenyl rings) does not induce any change in the oxygen quenching degree. In both sets of compounds, the thermodynamic feasibility of oxygen quenching is the same for the hemicaged and open compounds, thus giving evidence of the structural origin of such quenching decrease. The SPQRopens up new routes to the design of tailored, more or less sensitive to oxygen, luminescent iridium complexes (e.g., for use as biolabels). A family of four tris(2-phenylpyridine)-based Ir III complexes with hemicaged or open (without capping unit but with similar functional groups on the ligand) structure are reported. Within the context of the parent tris(2-phenylpyridine) and the full-cage iridium(III) complexes, structure-photoluminescence quenching relationships (SPQR) of the four complexes have been investigated. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Flow properties of polymeric powders for selective laser sintering
No full textThe effect of temperature on the flow properties of three different polymeric powders was assessed in order to properly take into account real temperature conditions relevant to Selective Laser Sintering (SLS). Shear tests were carried out at temperatures from ambient conditions to values close to the melting temperature of the polymers. Tested flowability significantly worsens at temperatures 20–30 °C lower than the powder melting point. These results are consistent with the working temperatures identified by SLS machine users, but powder flow properties estimated at finite consolidation cannot be directly used to infer on powder spread-ability. Instead, when the average intensity of the interparticle forces is calculated from the powder flow properties, the derived granular Bond number correlates well with the most suitable process conditions experienced for these powders. In particular, Bond numbers lower than 100 are required for a satisfactory powder layer formation after spreading with the use of a blade
Unknown artworks and further considerations regarding Paolo de Matteis, Giuseppe Simonelli, Lorenzo Ruggi and other followers of Luca Giordano
No full textCientos de pinturas napolitanas de los siglos XVII y XVIII han sido generalmente atribuidas a la escuela de Luca Giordano, quien tuvo un largo número de alumnos cuyos nombres han sido transmitidos por las principales fuentes de la historiografía artística. A algunos de ellos, como Franceschitto o Monsù Anselmo, no les podemos asociar ni siquiera con una obra. Por el contrario, hay casos de seguidores anónimos de Giordano con un estilo reconocible, como el autor de las dos versiones de Santiago el Mayor, una conservada en Casalnuovo de Nápoles y la otra en Lecce. Otras obras siguen fielmente el estilo de Giordano y llevan la firma de pintores que serían de otro modo desconocidos, caso de Lorenzo Ruggi, que firma una hermosa Inmaculada en la iglesia de S. Franciscode Aversa. Otro notable artista seguidor de Giordano es el «G. Fatteruso» que firma el Milagro de San Biagio en la iglesia de San Biagio en Mugnano de Nápoles. Es sin duda plausible la identificación con Giuseppe Fattorusso, recordado como discípulo de Vaccaro y luego de Beinaschi, si bien la comparación con sus obras documentadas plantea algunas dudas. Por último, una revisión de obras de diversa calidad, atribuidas con reserva a Luca Giordano o a su taller, puede arrojar una nueva luz sobre la cuestión de las numerosas imitaciones de las obras del maestro. La calificación de copias sería la más adecuada, por ejemplo, para las dos versiones de la Bendición de Isaac aparecidas en el mercado anticuario de Nueva York y en una colección privada en Sant’Arpino.Hundreds of 17th- and 18th-century Neapolitan paintings have been generically attributed to the school of Luca Giordano, who had many pupils, whose names have become known to us thanks to the leading historiographical sources of Neapolitan art. The work of some of these artists, such as Franceschitto and Monsu Anselmo, is unknown, although there are some anonymous Giordano followers who can easily be identified by their style, among them the author of two versions of St James the Greater, one of which is kept in Casalnuovo di Napoli and the other in Lecce. In addition, there are other works that are heavily influenced by Giordano and signed by hitherto unknown artists. These include Lorenzo Ruggi, who painted the wonderful Immaculate adorning St Francis Church in Aversa. Recent documentary research has revealed some information on the painter. Another leading follower of Giordano’s is one “G. Fatteruso”, who completed the majestic Miracle of St Blaise at St Blaise Church in Mugnano di Napoli. Though there are obvious grounds for identifying this artist as Giuseppe Fattorusso,remembered as a pupil of Vaccaro and later of Beinaschi, comparisons with the latter’s documentedworks suggest that this is not the case. Finally, newly conducted analysis of poorer-quality paintings that are cautiously attributed to Giordano or his studio, has enabled more detailed investigation into the problem regarding copies of Giordano’s famous works. Examples of this are two depictions of The Blessing of Isaac, one sold in New York and another in Sant’Arpino (near Naples), both of which can only be regarded as copies of a lost Giordano composition
Mise en œuvre de poudres de polyamides : Influence des conditions de transformation sur la microstructure et les propriétés. Application à la fabrication additive par fusion laser.
No full textSelective Laser Sintering, also called Powder Bed Fusion, is an additive manufacturing process that transforms a polymer powder layer-by-layer by melting with a laser beam scanning specific areas of each layer. The stages of transformation of a semi-crystalline polymer by laser fusion are: the flow of the powder at high temperature, the melting-coalescence of the particles, the resorption of the porosities and the solidification by crystallization during cooling. The most important parameters are the power of the laser and the temperature field in the manufacturing tank. The material undergoes high temperatures and thermal variations whose kinetics are still poorly known. The cohesion of the successive layers and the microstructure of the manufactured object (porosity, crystallinity) depend on these complex thermal conditions. The relationships between microstructure, final properties and thermal history of the material are not fully understood. In this work, two powders of polyamides (PA 6 and PA 12) are studied. First, the physical processes described above are analyzed under laboratory conditions with a controlled thermal history. This makes it possible to better understand and to model the role of the intrinsic properties of the polymer in the physicochemical phenomena involved in its transformation at different scales. This study gives access to the time scales of these mechanisms, as a function of temperature, and to the resulting microstructures. Then, parts are produced by two methods of powder melting, one in the laboratory on a hot plate, the other in an industrial SLS machine. Knowledge of the characteristic times of coalescence, evolution of porosities and crystallization enables to explain the microstructure and the mechanical properties of the objects in relation to their production method and the associated thermal history. This analysis sheds new light on the development of microstructures of polyamides transformed by laser fusion and the resulting properties.La fusion laser est un procédé de fabrication additive transformant une poudre de polymère, déposée couche par couche, par fusion grâce à un faisceau laser balayant des zones précises de chaque couche. Les étapes de transformation d’un polymère semi-cristallin par fusion laser sont : l’écoulement de la poudre à haute température, la fusion-coalescence des particules, la résorption des porosités et la solidification par cristallisation lors du refroidissement. Les paramètres prépondérants sont la puissance du laser et le champ de température dans le bac de fabrication. Le matériau subit des températures élevées et des variations thermiques dont les cinétiques sont encore mal connues. La cohésion des couches successives et la microstructure de l’objet fabriqué (porosité, cristallinité) dépendent de ces conditions thermiques complexes. Les relations entre microstructure, propriétés finales et histoire thermique du matériau ne sont pas complètement élucidées. Dans ce travail, deux poudres de polyamides (PA 6 et PA 12) sont étudiées. Tout d’abord, les processus physiques décrits plus haut sont analysés dans des conditions de laboratoire avec une histoire thermique contrôlée. Cela permet de mieux comprendre et de modéliser le rôle des propriétés intrinsèques du polymère dans les phénomènes physicochimiques de sa transformation aux différentes échelles. Cette étude donne accès aux échelles de temps de ces mécanismes, en fonction de la température, et aux microstructures qui en découlent. Ensuite, des pièces sont produites par deux méthodes de fusion de poudre, l’une en laboratoire sur plaque chauffante, l’autre en machine industrielle de fusion laser. La connaissance des temps caractéristiques de la coalescence, de l’évolution des porosités et de la cristallisation permet d’expliquer la microstructure et les propriétés mécaniques des pièces en relation avec leur méthode de production et l’histoire thermique associée. Cette analyse apporte un nouvel éclairage sur le développement des microstructures de polyamides transformés par fusion laser et les propriétés qui en découlent
Processing of polyamide powders : Influence of transformation conditions on microstructure and properties. Application to additive manufacturing by laser sintering.
No full textLa fusion laser est un procédé de fabrication additive transformant une poudre de polymère, déposée couche par couche, par fusion grâce à un faisceau laser balayant des zones précises de chaque couche. Les étapes de transformation d’un polymère semi-cristallin par fusion laser sont : l’écoulement de la poudre à haute température, la fusion-coalescence des particules, la résorption des porosités et la solidification par cristallisation lors du refroidissement. Les paramètres prépondérants sont la puissance du laser et le champ de température dans le bac de fabrication. Le matériau subit des températures élevées et des variations thermiques dont les cinétiques sont encore mal connues. La cohésion des couches successives et la microstructure de l’objet fabriqué (porosité, cristallinité) dépendent de ces conditions thermiques complexes. Les relations entre microstructure, propriétés finales et histoire thermique du matériau ne sont pas complètement élucidées. Dans ce travail, deux poudres de polyamides (PA 6 et PA 12) sont étudiées. Tout d’abord, les processus physiques décrits plus haut sont analysés dans des conditions de laboratoire avec une histoire thermique contrôlée. Cela permet de mieux comprendre et de modéliser le rôle des propriétés intrinsèques du polymère dans les phénomènes physicochimiques de sa transformation aux différentes échelles. Cette étude donne accès aux échelles de temps de ces mécanismes, en fonction de la température, et aux microstructures qui en découlent. Ensuite, des pièces sont produites par deux méthodes de fusion de poudre, l’une en laboratoire sur plaque chauffante, l’autre en machine industrielle de fusion laser. La connaissance des temps caractéristiques de la coalescence, de l’évolution des porosités et de la cristallisation permet d’expliquer la microstructure et les propriétés mécaniques des pièces en relation avec leur méthode de production et l’histoire thermique associée. Cette analyse apporte un nouvel éclairage sur le développement des microstructures de polyamides transformés par fusion laser et les propriétés qui en découlent.Selective Laser Sintering, also called Powder Bed Fusion, is an additive manufacturing process that transforms a polymer powder layer-by-layer by melting with a laser beam scanning specific areas of each layer. The stages of transformation of a semi-crystalline polymer by laser fusion are: the flow of the powder at high temperature, the melting-coalescence of the particles, the resorption of the porosities and the solidification by crystallization during cooling. The most important parameters are the power of the laser and the temperature field in the manufacturing tank. The material undergoes high temperatures and thermal variations whose kinetics are still poorly known. The cohesion of the successive layers and the microstructure of the manufactured object (porosity, crystallinity) depend on these complex thermal conditions. The relationships between microstructure, final properties and thermal history of the material are not fully understood. In this work, two powders of polyamides (PA 6 and PA 12) are studied. First, the physical processes described above are analyzed under laboratory conditions with a controlled thermal history. This makes it possible to better understand and to model the role of the intrinsic properties of the polymer in the physicochemical phenomena involved in its transformation at different scales. This study gives access to the time scales of these mechanisms, as a function of temperature, and to the resulting microstructures. Then, parts are produced by two methods of powder melting, one in the laboratory on a hot plate, the other in an industrial SLS machine. Knowledge of the characteristic times of coalescence, evolution of porosities and crystallization enables to explain the microstructure and the mechanical properties of the objects in relation to their production method and the associated thermal history. This analysis sheds new light on the development of microstructures of polyamides transformed by laser fusion and the resulting properties
Tuning brightness and oxygen sensitivity of Ru(II) and Ir(III) luminophores
No full textThe design of luminophores with high brightness is of crucial importance for many applications like the realization of Organic Light Emitting Diodes (OLEDs), and for biomedical imaging. However, despite the great number of works dedicated to the definition of the possible strategies for the realization of bright compounds, we are still far from a "perfect" luminophore for biological applications. The design of highly bright luminophores for biological imaging still constitutes a major challenge: the necessity of conjugating a high brightness (the product of the quantum yield and the molar extinction coefficient) with a low degree of oxygen quenching (which is necessary in order to keep a high luminescence in the oxygen-rich bio-environment) is still an open problem. Semiconductor Quantum Dots (QDs) are so far, the best candidates for biological applications since they show quantum yields closed to the unity and low oxygen sensitivity. However, despite the brilliant performances shown by QDs, their in vivo toxicity is still a major concern, especially from the perspective of a human application. Transition metal complexes are ideal candidates for the realization of bright luminophores, considering their high stability in biological environment and the possibility of tuning their optical properties by conveniently changing the structure of the ligands. Ruthenium(II) and iridium(III) complexes, in particular, are among the most studied transition metal complexes and the large amount of literature available makes them ideal candidates for further improvement. Two possible strategies can be followed in order to improve the optical properties of a luminophore: the decrease of its oxygen quenching degree and the amplification of its brightness. The first strategy is quite promising especially in order to improve the optical properties of Ir(III)-complexes, which show a pronounced oxygen sensitivity. Conversely, the brightness amplification via multiple labelling is particularly attractive for Ru(II)-complexes, which are barely sensitive to oxygen quenching but show also a low emission quantum yield. In this thesis both strategies have been applied in order to realise highly bright luminescent compounds based on Ru(II) or Ir(III) complexes. Moreover, since there is only a limited amount of literature concerning the tunability of the oxygen quenching of Ir(III)-complexes, a systematic study has been conducted in order to clarify the structure-quenching relationship
Safety of Adjuvanted Recombinant Herpes Zoster Virus Vaccination in Fragile Populations: An Observational Real-Life Study
No full textVaccination is the most effective strategy for preventing infectious diseases
and related complications, and proving its efficacy is crucial for its success and adherence, especially
for newly introduced vaccines, such as adjuvanted recombinant herpes zoster virus vaccination
(RZV). In this observational real-life study, we recorded adverse effects following immunization
(AEFIs) after RZV administration in frail populations. Methods: A total of 271 subjects underwent
RZV at Vaccination Center, University Hospital “San Giovanni di Dio e Ruggi d’Aragona”, Salerno,
Italy. Most subjects were solid organ transplant recipients (kidney, 77.1%; liver, 4.8%). Demographics,
clinical data, and AEFIs (type, duration, and medications used) were recorded. Results:
Overall, 37% of participants reported at least one AEFI following the first dose, predominantly pain
at the injection site (60%), while 41% did so after the second dose (pain at the injection site in 62%
of cases). Medications were more frequently used for AEFI treatment after the second dose (28%)
rather than after the first dose (13%) (p = 0.01). After stratification by sex, females experienced AEFIs
more frequently than males, particularly local skin reactions. Conclusions: Our study added evidence
of safety and tolerability of the adjuvanted recombinant RZV in frail adults
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